It's called seignorage. In fact, Satoshi explicitly said:
I think this is a nice advantage vs fiat currency, instead of all the seigniorage going to one big entity, let it go in convenience amounts to people who need to scrape up a small amount of change.
In fiat economies I think that the majority of price inflation is basically a government-imposed wealth tax via money-printing, but some inflation is caused by other factors. For example, you could design (and I have elsewhere sketched out) a cryptocurrency based on debt, similar to government fiat currencies, but totally fair without any government skimming off the top; but due to the way these currencies work, you still need a small inflation rate (maybe 0.5%) to make it work. Some inflation can also be caused (even with a BTC world reserve currency) by things like oil price increases or changing market interest rates, though the long-term trend should be deflationary due to constant tech improvements.